Acceleration problems with my baby

[woody]

Hi All; Ive had my mighty Valk for about 9 years and had a great time. I live down under in Australia and its just coming into the best riding time of the year. But I have had a little problem for the last few months.
As I accelerate, the bike goes great with gradual acceleration right up to redline without pause.
But if I give it full throttle at medium to low revs it hesitates or lacks power. If I back off the throttle just a little it goes back to accelerating quite well.
I have changed the air filter, syncronised the carbs, added fuel cleaners for several tanks and adjusted the valves. Everything appears perfect except for the lack of acceleration at full throttle.
Please help me get my beautiful machine running perfect again
Woody

[MP]

You may well need a cover set.  That is the repair for the diaphram in the petcock.  If the rubber has a small tear, it will be OK except for when you need max fuel.  Sounds like that is what is happening to you.  About $27 US.  "Cover Set" is what you want.
MP

[woody]

Thanks for that, Ill get one so I can replace it.
Ill let you know how it goes.

[Valker]

You either have a blockage in the fuel line or air intake. You might look and see if the tank vent tube has been plugged by an insect and that the "T" fitting is still open on one side. The fuel screen inside the tank may be clogged. Right now, at the end of your summer, I would guess the air being plugged. You may have let the drip tank under the bike fill too much (but i hear your weather has been very dry-so maybe not). Easy to unscrew the plug and check though. You can test the tank vent being plugged by leaving the cap slightly open on a run where it does this. That will let the tank vent properly. ???
If the fuel valve is OK (like the other poster says) try these.

[Scott from FL, now in Maine]

Fully agree with the above posts. I would also suggest you check the vacuum to the petcock. I think something sounds wrong with the fuel flow. Hope it is something simple.   

[woody]

I have replaced my air filter thinking that it may have been the K&N filter....no Joy
I syncronised my carbs thinking that it may be that...no joy
I checked and adjusted my valves (max error was less than a thou of an inch) ...no joy
New plugs, new fuel and fuel additive to clean (4 tanks).....no joy.
I was thinking perhaps coil failure under load, but Ill try the petcock first a its still the easy option, and i have not heard of any Valks coils failing.
I will also check and probably replace all vac hoses, as you have suggested, this would be sensible.
It realy is helpful with your suggestions, thanks heaps.
It is dissapointing that such a beautiful motor is not running at its best, with luck and all your help, perhaps soon it will.

[Airetime]

Cracked hoses! If you have not replaced them in 9 years, that's the problem I'll bet!  They are probably collapsing under full throttle. Use a little starter fluid or WD40 and spray on the vaccum lines and if it accelerates, replace the hoses.

[DFragn]

I would also inspect all six carb diaphragms under the carb covers.
A small pinhole or tear can present similar to your issue. They're somewhat delicate, so be careful and hold them up to a bright light for inspection if you choose to do so.

[woody]

Never thought of the carby diaphragms, thats a great suggestion.
I think Ill replace the vac hoses regardless, as you say 9 years is a long time sitting on a hot motor.
I've been thinking, if the petcock was a problem, wouldn't it be a gradual loss of power instead of a flat spot instantly? I suspect there should be sufficient fuel in the carbs to at least keep on full throttle for a few seconds?
The symptom is more like turning a switch on and off. Full throttle lacks acceleration and backed off a little (as much as a 16th turn) starts accelerating again, give it full throttle and we are back to a flat spot.
Also, if I knock it back a gear and pull on full throttle (thus reducing the load on the engine due to higher revs), it revs out to redline without pause or hesitation.
To reinterate, it appears to lack power only at full throttle under load.
The carb diaphragm would give instant feedback as described as would the vac hoses I think.
Has anybody had similar problems?

[Zorba]

Just for kicks star the bike up in a dark garage and rev it up and see if your plug wires are arcing, if so you'll see a small light show!

Don't think you have a "jet" problem?
Your "Main jets control the gas from 1/2 throttle to full throttle but i assume they are clean since you ran additive in the bike!

If it was coil it would only effect certain cylinders and sometimes a bad coil will make the engine "knock" just like a lifter so probably not coil!?
First check that diaphram on the petcock and make sure your intake rubbers ain't leaking?

[woody]

Thanks guys, I now have a list of things to do this weekend.
I have never had any knocking so I can reasonably eliminate that.
First start bike in the dark and look for arcing.
check carbs.
remove tank and check petcock
Replace vac hoses and drain hoses just for consistency
finally if this does not cure the problem Ill check the intake rubbers.
Looks like a busy weekend.
As we say in Australia. Avagoodweegend and Stay upright.
 

[AussieValk]

Hey Woody, I'm having similar problems accelerating under load. Getting that flat spot at about 3500 to 4000rpm. I've ordered the cover set here in Aus. Cost $61 locally sourced from Honda Australia. There is an issue with the part numbers so quote both the old and new if you order. Old: 16953-MV9-000 and new: 16953-MBZ-B51. They have four left in stock now...

Where in Oz are you located, was it SA? I'm wondering if the extreme heat we've had this summer has had something to do with the problem. I'm based in Qld. It'd be good to talk to someone closer to home.

[woody]

Hi AusieValk, Im down south in Newcastle and yeah we have been getting the same heat as you guys, (40+ cel), but this is not a problem to me because I dont ride in that heat, my screen keeps all the heat around me and I cook.
The problem I have has been coming on more gradual over the last few months, initially it was only slight, but its becoming more and more annoying as time goes on.
I do tend to leave my bike sitting, sometimes weeks at a time as I travel all over Australia for my job and it gets hard to find time to ride it, but its been that way for the 9 years I have owned it so why the problem now?
The guys on this tech talk have been great, Im planning to replace the hoses this weekend and check out all the other things suggested, Ill post a note when Ive done it to let everyone know how it went.
Problem is that Im off across Aus next week so if I havn't finished it this weekend it may be a while.
I get up to Qld about once every 6 weeks or so, Brisbane mostly, if I fix the problem I can visit and show you what to do if you like. Thanks for the advice on the Kit part numbers, I had some difficulty in getting through to the parts dealer what I wanted, I suspect there are very few Valks in Newcastle.
Cheers all.

[sugerbear]

the real problem is your bikes are upside down, down there. you'll need fuel injection to cure that LOL  
sorry couldn't help it.

[woody]

ooohhhhh, That explains why all my money falls out of my pocket.
Does that mean I dont fall off my bike, the earth falls on me?
Seriously though, I have considered Fuel injection, but then I thought "it ran perfectly before, why change it?"

[AussieValk]

Problem does sound more like vac lines if its gradual. Mine was sudden and happened about two months after having carb sync and valves adjusted. Was running sweet before that. I sent you a PM with contact details if you're ever up this way.

Cheers.

[5_19]

Sounds like petcock problem to me! Thats if my memory is correct~TJ

[Zorba]

If the bikes are "upside down" then the forks are rightside up, should ride better,lol!

[sugerbear]

 

[Oss]

I am ordering that hose as well

Not to hijack the thread but I have a Question for you Woody.  I know the Valks in Japan had reverse.  Have you seen any in Australia with the reverse?

Good luck with the repair this weekend   I look forward to hearing how it went

Oss

[woody]

Hi Oss, I have seen very few Valks in Australia. Even on runs there have been fewer than 4 or 5 at a time. Of those, I have never seen or heard of a valk with reverse.

Just an update; I had the airfilter off last night and checked the petcock diaphragm, it had no damage or problem operating the fuel. I put a vaccum on the line and left it for 1/2 hour and it still had the same reading after that time.(I put a "T" piece on a hose between the valve and a gauge and sucked on the open pipe, when I had a reading I plugged the end and read the reading and left it) Im assuming this is not the cause.
I also took each of the carbs diaphragms out and checked them for damage or holes, none found, even stretching the diaphragm slightly. The carbs and needles were very clean and like new.No problem there I think.
However, the vac hose to the petcock had collapsed a bit and each of the vac lines on the carbs were cracked around the ends and very brittle. Im thinking this may be my problem.
All vac hoses will be replaced tonight, also fuel lines and drain hoses. Ive got the airbox off so I might as well do it while its open.
Just to make sure Im also changing the plugs, putting fuel cleaner through the tank, checking the timing and advance and syncing the carbs.
I would just like to thank you guys, I would never have thought to look at the vac lines and and some of the other things. It would have probably cost me a fortune to have someone else fix it for me.

[johnny kiwi]

Woody the same thing happened to me. Im from NZ and have the 97 Aussy model Valk No. 8 (serial number). Anyway I followed all the good advice from the others. Cleaned my Carbs, checked the petcock ... but the answer was much easier. In the intake of the air box above the filter there is a thin piece of foam which restricks the air flow. In mine when the problem occured it was sudden and of course I at first thought it was a fule blockage but decided it felt like not one jet but an overall thing so I pulled the air box apart while checking for a fuel filter. I of course removed the fule tap and cleaned the filter but when checking the air filter I found the thin foam screen on top of the paper filter but thouht it wasnt important, and as it had disendgrated I discarded it and put the bike back together with no change in performace. Yes I could still get 180km out of her as long as I did it slowly, but a big handful it choked out at around 3500 to 4500rpm. The fix was to tape some womans panthose across the intake. (get the woman to remove them first). I used a double layer and the problem was fixed. I read La Monsters article on re-jetting the valk which mentions the air box and how you should leave it stock standard. Today I just fitted my new K&N filter and removed the stocking thinking I should be sweet but no. Its not as bad as it was but Im going to have to get the piece of foam or put the stocking back on. I did look for the part at the honda dealer but it wasnt listed whic was another reason I thought it wasnt that important. Give this a go bet you it fixes it :

[woody]

Hi All, some good news and some bad.
All vac hoses were cracked and probably leaking air, replaced.
Petcock valve was perfect and held a vac for over an hour before I got bored and stopped the test.
Timeing was perfect, and "Boston rats" the advance also was correct on all coils (thanks anyway)
There was no lead breakdown (Zorba) in fact it looked perfect. Just for a test I pulled each plug and stuck a screwdriver in the lead and placed it near the engine to test the spark, it jumped about 3/8" with no problem and about 1/2" intermittently. By the way it hurts when you become the conductor.
Carb diaphraphms were also clear and no holes or tears.
New plugs made no difference at all, either did a new air filter.
With all things checked and replaced, I went for a ride. The mighty Valk was a bit better, but it still had the same problem.
It does idle better, and runs better up to the dead spot, but it still performs less than ideally.
I have just noted a new check from "Johnny Kiwi" to do with a sponge in the air filter box. Sounds like an air restriction device. I was the first to open the airbox and it wasnt in it from new, but Ill try it and see what happens.
I am running some carb cleaner (complete fuel system cleaner) (I couldnt find and techtron in Aust) for a few tanks and if it dosent improve I plan to pull the carbs out and clean them.
I have noted that larger main jets have been mentioned in other postings to the tech talk, has anyone tried them?
Thanks for all your help, still not giving up!!!!!

[f6john]

Just for giggles, raise the front of the tank and put a 1/2" spacer under the tank mount and go for a ride.

[woody]

Hi Bostorats, I cant say for sure it was 20 deg, but it moved considerably when I reved it up. I used a xenon? timing light and had to pull the plug leads off the plugs a bit to get enough signal through the pickup to get a good consistent flash (I think all the metal around the pickup affected it). The timing and advance was as near to identical as it could be on all 3 coils.
f6john, I think I know where you are coming from, but I have drained the fuel, pulled out the fuel tap and cleaned everything. There was no water or crap on either the filter or in the tank.
By the way, if you dont turn the fuel tap on when you go for a ride the bike performs very badly. It pops and misses and finally dies. Took me 5 minutes to work out what was wrong. (I never said I was smart!!!)

[woody]

Hi Bostonrats;
The bike has just short of 50,000klm on the clock. Easy highway miles most.
I always use the best oil (synthetic) and carry out services by time rather than miles. I do leave it for reasonably long periods just sitting.
Stock needles, Stock exaust, No engine mods. I checked the valve adjustment, there was only one valve which was an exaust valve out by .001", but that could be just my feel. Checked the cam timing and it is also correct to the book.
As you describe, Slow gradual acceleration ...all the way to redline. Grab a fistful under load it hesitates, but if you shift down it runs to redline until it hits the rev limiter.
Ive also noticed that you can get to a point about 1/4" before full throttle and fiddle between acceleration and dead spot just by twisting the throttle a fraction.
Ive never snapped the throttle to full from idle without the bike gears engaged, it revs to quickly.
I like the idea of checking the float levels, I have had this problem on other bikes, so Ill be checking this later this week.
I had each of the diaphragms out and had a good look at the needles and what I could see of the jets and body, they were clean and unmarked.
I have no compression tester, but Ill try and get one to check it.
It does sound a bit of a pain to check the carbs, but I plan to pull the carbs out if I cant get it running right and cleaning them, so the check you describe would not be much of an issue. I had the airbox out on the weekend and it wasnt too bad.
The timing belt looks like new and is as tight as it was when new. the marks all line up and from what I see there is no issue there.
The bike dont loike choke, I tried what you suggested thinking along the same line, but it just felt sluggish until I turned it off.
I haven't tried sniffing the exaust, but Im running a fuel system cleaner at the moment and I know it smells a bit anyway. I try that when this tank is finished.
You are a great help, thanks.
Ill keep you posted on how it goes. But ive got the feeling Ill have to pull down the carbs to fix my problem.
The plugs were all a nice tan on the insulator with a light dusting of carbon on the metal screw end, again nothing wrong as I see it.

[woody]

And at the end of the day there are always matches, and with all that fuel around it would really fly!
Looks like Im going to be busy, but Im travelling this week so I will not have time to check them until the weegend. Ill log on next week.
Have fun and thanks again.

[R J]

Someone above said raise the front of the tank about a 1/2".

They were not being a smart ass, there was a reason they said that.............

I raised mine a 1/2 with a spacer and a longer bolt.

You can go to BIGBF.COM and have a look see at what he built and sells.........

Mine used to have a flat spot also, and ya had to back off the throttle, but since I raised the tank, I can hit the full throttle and then hang on for dear life.........  MGM will flat arsed fly now.......  Mine was not getting enough air......

[John U.]

Hey RJ
Does raising the tank 1/2" cause any tank instability? Seems like if the tank was raised the rubber bumpers attached to the left and right frame rails would no longer be able to steady the tank.
I was thinking of gluing rubber pieces maybe 1/4 to 3/8" thick to make up that additional space.

Back to Woody's problem. Seems like if a bit of choke (enrichment) did nothing to improve the situation then the trouble is not likely to be fuel starvation, assuming correct fuel levels in the bowls. That is unless fuel flow from the tank is the culprit. I think Woody said no engine mods, would that include a fuel filter, how about a dirty screen?
Has anyone mentioned intake tube O-rings as a possible cause of vacume leaks? How about the clamps attaching the carbs to the intake tubes?
Seems like everything else has been covered, except, I know the vacume lines have been replaced, how about the vacume caps?  They can leak too. I know these are minor things, just covering the bases.

[Ricky-D]

Consider the gasoline you are having to use. Maybe there has been a change?  About the dead spot. If you start right off, from stopped (or slow) can you accelerate right on through it or will it appear regardless?  That bit about raising the tank is cogent. What is being said is that you could have a pinched gas tank vent line that is restricting gas flow and raising the tank is one way to relieve that problem. Can you answer my question and we'll go on from there.  You could also index the throttle to help with the problem.

[John U.]

The point about tank venting is certainly valid, but I don't believe the suggestion about raising the front of the tank refers to venting if the tank. It's about relieving possible air starvation by the engine at full throttle. I haven't done the tank spacer mod myself, so I can't say how much difference it would make.

[sugerbear]

raising the front of the tank (i used a stack of washers, wrapped in electrical tape) did make a difference in my 2k I/S. not much, but some. stability is the same as no washers.

[Ricky-D]

Regarding your intention to check float levels: They are non-adjustable. Have to be replaced, and that would be if a float fails to stop the gasoline from flowing because of a leak in the float. (like a sinking float)

[Beer van Huet]

I have a similar problem with acceleration after taking the Air Box off. I removed the foam pad on top because it was worn.  I wonder if the foam pad has just a filtering function or that it also causes an initial rich mixture (because less air can get through) during rapid acceleration. Is anyone riding without the foam pad in the airbox top and could this make a difference?

TIA,

Beer

[f6john]

Hi Bostorats, I cant say for sure it was 20 deg, but it moved considerably when I reved it up. I used a xenon? timing light and had to pull the plug leads off the plugs a bit to get enough signal through the pickup to get a good consistent flash (I think all the metal around the pickup affected it). The timing and advance was as near to identical as it could be on all 3 coils.
f6john, I think I know where you are coming from, but I have drained the fuel, pulled out the fuel tap and cleaned everything. There was no water or crap on either the filter or in the tank.
By the way, if you dont turn the fuel tap on when you go for a ride the bike performs very badly. It pops and misses and finally dies. Took me 5 minutes to work out what was wrong. (I never said I was smart!!!)

Actually what raising the front of the tank does is to allow more air into the airbox intake. I have a completely stock intake box no mods. I had installed an ACE Supertank and after several thousand miles I developed a condition to where in any gear it would run like a scalded dog up to 3500 rpm. Then if would just nose over, no power or acceleration above that. I could not figure it out and took it to my dealer who has a 20 year tech on staff and after 2-3 weeks he gave up after talking to some of the factory contacts he has. There had been some discussions on the old board about improving air flow and I knew I had either a fuel or airflow problem. Some of the guys were shimming up the front of the tanks, some for v-stack clearance some for air. I thought what the heck, added a 1/2 rubber washer spacer and shazammm, it worked. Dealer tech couldn't believe it. You don't have a supertank but it couldn't hurt to try. I should have explained all this in my earlier post, too lazy I guess. 

[AussieValk]

I have a similar problem with acceleration after taking the Air Box off. I removed the foam pad on top because it was worn.  I wonder if the foam pad has just a filtering function or that it also causes an initial rich mixture (because less air can get through) during rapid acceleration. Is anyone riding without the foam pad in the airbox top and could this make a difference?

TIA,

Beer

Good point. I was having the same trouble. My problem was a 1/4" split in petcock diaphram so it was replaced and I got my power back, well almost all of it. I have been running without the prefilter for sometime, but maybe that is the final part of the puzzle for me. I did hear of another bloke down here who had the same problem and his bike wouldn't run at all without the prefilter. If you think about the problem though, if it's not enough air and you take out the prefilter, shouldn't that compensate with the additional freeing up of airflow. I don't think Woody said it was running rich. Makes sense that the bike being stock should require the prefilter for optimum performance.

[johnny kiwi]

Hi Woody, mines a stock 97 Valk with 50,000 on the clock and I tried every thing mentioned in the above. I just put the stocking back over the air intake with my new K&N fitted and shes sweet again. Believe me when I say I was pulling my hair out trying to solve the problem. Has your air box (top cover) got the pre filter in it? Its about 5mm thick grey foam piece. I know it sounds too simple but everything you say sounds exactly like mine. I spoke with the honda mechanic today as the part ani't available on its own. He told me I could rejet but I think Ill stick with the stocking for now as its much easier. Try it, takes 10mins cost about $3. Youll know straight away. Ive had no other problems at all. By the way I tried some thick foam first but it was too much, but the stocking worked a treat. I wonder if the Americian friends with all the air emission stuff on thier bikes is slightly different?
cheers

[Tundra]

Three differant Valks, all K&N, no pre-filter, no problem.

[R J]

Hey RJ
Does raising the tank 1/2" cause any tank instability? Seems like if the tank was raised the rubber bumpers attached to the left and right frame rails would no longer be able to steady the tank.
I was thinking of gluing rubber pieces maybe 1/4 to 3/8" thick to make up that additional space.

 

The tank raised up doesn't have any more side to side movement that it did setting flat on the steer head....

Make sure the spacer is at least the same size as the one BigBF sells..........    If memory hasn't failed me, it is at least the same size as a silver dollar.   

If it fills the cavity in the tab, you is good to go.

[Beer van Huet]

I am not much of a mechanic, so I was afraid of taking the carbs apart. It never occured to me that carbs could be 'cleaned'  by blowing compressed air through the fuel hose with the drains removed. I got rid of 9 years of crab and pollution in just a few minutes and my engine revs like new again.

Thanks for the great tip; you've been a big help.

Beer